In the sentence above, Mr. Johnson could have replaced "their" with "his or her," or he could have said, "At this point, all control room engineers are on their toes."

Note: "None" used to be treated strictly as singular, because it is a contraction of "not one," but these days, says Harbrace6a(7), "When used as subjects, "all," "any," "some," and "none" may take either a singular or a plural verb, generally depending on the context.